Protective headwear to reduce risk of injury

ABSTRACT

A helmet configured to protect a human head against mild traumatic brain injury upon impact includes an outer shell and a liner consisting of fluid fillable flexible fluid chambers fluidly connected to each other by fluid connections. The fluid chambers being spaced around the circumference of the helmet and configured to fill a space between the head and the outer shell when the helmet is positioned on the head. Impact resistant flexible pads are also in the liner and are spaced around an inner circumference of the outer shell adjacent to each of the fluid fillable flexible fluid chambers. A flexible inner shell inside the liner is configured to fit closely on the head. The flexible fluid chambers are configured to compress in response to impacting of the helmet on an impact side and to force liquids through the fluid connections to inflate other fluid chambers inside the helmet thereby cushioning the head against a rebound impact on the inside of the helmet.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation-in-part of U.S. application Ser. No.15/227,593 filed Aug. 3, 2016 for “Protective Headwear to Reduce Risk ofInjury” by W. H. Tuttle and L. C. Whitaker, which in turn claims thebenefit of U.S. Provisional Application No. 62/203,152 filed Aug. 10,2015, both of which are hereby incorporated by reference in theirentirety.

BACKGROUND

This invention relates to protective head gear. In particular theinvention is a helmet designed to protect against mild traumatic braininjury (MTBI).

Traumatic brain injuries can occur when the head experiencesaccelerations or decelerations that cause the brain to move within theskull and generate physical damage to structures within the brain. Theaccelerations associated with traumatic brain injuries can be linear,rotational, or complex combinations of accelerations. The brain is asoft gelatinous organ housed within the skull surrounded by liquid.During a high speed acceleration event the brain can move within theskull and impact the skull and subsequently rebound and experienceadditional impact with the skull on the opposite side of the brain(coup-contrecoup). In lower speed acceleration events the brain may notimpact the skull, but can still sustain damage as the internalstructures of the brain slide past each other and damage neuralinterconnections.

These injuries are generally referred to as mild traumatic braininjuries (MTBI). The word mild refers to the manner of impact and notthe severity of the injury. The term concussion is often used todescribe mild traumatic brain injuries. Symptoms of concussion caninclude loss of consciousness, headaches, confusion, temporary cognitiveimpairment, vertigo and balance problems. More severe mild traumaticbrain injuries can cause permanent impairment and increased risk ofserious long term medical complications. Repeated mild traumatic braininjuries are associated with additional long term health risks includingneuro degenerative brain diseases such as chronic traumaticencephalopathy which has been found in former professional athletes whohave experienced multiple concussions over their careers.

Studies of the causes of concussions have demonstrated that a wide rangeof acceleration forces can cause concussions. For example, studiesindicate that American football players regularly sustain accelerationsof 20 to 180 Gs with various injury outcomes. In general the higher theG-force, the greater the injury, but some athletes have experiencedconcussions at impact forces below 60 G while others have been free ofconcussion injury at impact forces in excess of 100 G. 60 G is oftenconsidered a level below which it is unlikely that a concussive injurywill occur.

SUMMARY

A helmet configured to protect a human head against mild traumatic braininjury upon impact includes an outer shell and a liner consisting offluid fillable flexible fluid chambers fluidly connected to each otherby fluid connections. The fluid chambers being spaced around thecircumference of the helmet and configured to fill a space between thehead and the outer shell when the helmet is positioned on the head.Impact resistant flexible pads are also in the liner and are spacedaround an inner circumference of the outer shell adjacent to each of thefluid fillable flexible fluid chambers. A flexible inner shell insidethe liner is configured to fit closely on the head. The flexible fluidchambers are configured to compress in response to impacting of thehelmet on an impact side and to force liquids through the fluidconnections to inflate other fluid chambers inside the helmet therebycushioning the head against a rebound impact on the inside of thehelmet.

In an embodiment, a method of forming a helmet to protect a human headagainst mild traumatic brain injury upon impact includes forming anouter shell larger than the head and forming a liner consisting of fluidfillable flexible fluid chambers that fit inside the outer shellconfigured to fill a space between the head and the outer shell when thehelmet is positioned on the head. The method further includes connectingthe flexible fluid chambers with fluid connections such that at leasttwo fluid chambers are interconnected. The method further includesfilling the interconnected flexible fluid chambers with fluid andforming impact resistant flexible pads inside and spaced around theinner circumference of the outer shell adjacent to each of the flexiblefluid chambers. The method further includes forming a flexible innershell inside the liner configured to fit closely on the head andattaching the flexible fluid chambers and flexible pads to the inner andouter shells to form the helmet such that the flexible fluid chambersare configured to compress in response to impacting of the helmet on animpact side and force liquid through the fluid connections to inflateother fluid chambers in the helmet thereby cushioning the head against arebound impact on the inside of the helmet. The helmet is finished byattaching a chinstrap and fastener to the helmet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-section of a helmet according to anembodiment of the invention on a human head.

FIG. 2 is a top view of the liner of the helmet with the outer shellremoved.

FIG. 3 is a side view of a helmet with a strap.

FIG. 4A is a top view of an embodiment of the liner of the helmet withthe head centered in the helmet

FIG. 4B is a top view of the embodiment of FIG. 4A with the head rotated25° counterclockwise around the central axis of the brain.

FIG. 5A is a side view of an embodiment of the liner of the helmetpositioned on a human head facing right.

FIG. 5B is a rear view of the embodiment shown in FIG. 5A.

FIG. 6A is a side view of the embodiment of the helmet positioned on ahuman head facing right.

FIG. 6B is a rear view of the embodiment shown in FIG. 6A.

FIG. 7 is a side view of an embodiment of the helmet positioned on ahuman head.

FIG. 8 is a method of forming a helmet according to an embodiment of theinvention.

DETAILED DESCRIPTION

The present invention relates to protective headwear typically referredto as a helmet. Such a helmet fulfills the task of protecting a person'shead from injury in the case of impact with other objects. Protectiveheadwear is used in a variety of military, industrial, and sportingactivities to prevent, or reduce the severity of, traumatic injurycaused by foreseeable impacts associated with those activities. Forexample, participants in many sports such as American football,baseball, cycling, equestrian, field hockey, ice hockey, lacrosse,skiing, snowboarding, surfing, wakeboarding, and water skiing routinelywear protective helmets to reduce the risk and severity of head injuriesin general and traumatic brain injury in particular. Additionalactivities such as automobile racing, motorcycling, and snowmobiling aresports often associated with the use of specialized protective helmetsto protect the users from injuries including traumatic brain injuries.

Studies have demonstrated that the natural resonant frequency of thebrain within the skull is approximately 15 Hz. If an impact generatesaccelerations that excite brain motions at or near its natural resonantfrequency, the motions and impacts of the brain within the skull may beamplified and the damage caused can be greater than would otherwise beexpected for the G-force experienced. Thus there is a need forprotective helmets that will reduce the accelerations experienced by theusers' head and reduce the tendency of an impact event to amplify thebrain's motion at or near its natural resonant frequency. Prior art hasbeen generally good at limiting the peak acceleration forces experiencedduring impact. One method well known in the prior art is the use of aliner made from non-resilient compressible materials that permanentlydeform at selected force levels. This deformation absorbs energy andestablishes the maximum acceleration level that can be experiencedduring the time that the material is undergoing compression. Onelimitation of such helmets is that by only establishing a peak value,the helmets can offer insufficient protection from lower forceaccelerations that trigger resonant amplifications of brain motionswithin the skull. An additional limitation of such designs is that afterthey have functioned, the liner material has lost its protectivecapacity and must be replaced. The materials may not appear to have beendepleted and users may wrongly continue to rely on the helmet foradditional impact protection.

In a typical concussive event, the head is rapidly decelerated, causingthe brain to move within the skull. The brain is attached near itsbottom-center and can swing about this fulcrum. As the brain moves intocontact with the skull, it compresses and rebounds, contacting theopposite side of the skull. This can cause two injury sites in the brainand is referred to as a “coup-contrecoup” injury. Since the brain can beconsidered as an underdamped mechanical system, a method of protectionagainst coup-contrecoup injury is to supply damping to the system,particularly at the resonant frequency of the brain.

There is a need for protective helmets that can reduce the impact forcetransferred to a user's head in terms of reducing the peak forceexperienced and to control the effective frequency of the energytransfer to a value that does not tend to excite brain motionamplification at its resonant frequency.

A non-limiting embodiment of the invention is shown in FIG. 1. FIG. 1 isa schematic cross-section of helmet system 10 on human head 12containing brain 14. Helmet system 10 may include outer shell 16, amiddle liner containing fluid filled flexible fluid chambers such asbladders 18 and interconnecting fluid passageways 20, and inner liner22. The energy absorbing mechanism of helmet system 10 is as follows. Ifthe user is travelling forward and experiences a frontal head-on impactwith an object, head 12 will continue to move forward generatingincreased pressure in fluid filled bladder 18A at the forehead. Thehigher pressure will force fluid from bladder 18A to bladder 18E at therear of head 12 through fluid passageway 20. The fluid viscosity anddimensions of fluid passageway 20 may be sized to establish a rate offluid transfer during acceleration that may absorb impact energy andlengthen the time of the energy absorption process to reduce theeffective frequency of the energy transfer. This action may spread theforce over time and distance, to reduce the peak force experienced bybrain 14. It may also increase the time over which the brain experiencesthe force to well above the 33 millisecond half wave period of theapproximately 15 Hz resonant frequency of the brain.

An additional feature of helmet system 10 is shown in FIG. 2. FIG. 2 isa schematic top view of helmet system 10 with outer shell 16 removed.Compressible material 24 may be placed on each side of flexible fluidchambers 18A-18H in the middle liner. Inner liner 22 forms the insidelayer of helmet system 10. The purpose of these compressible devices isto center head 12 within outer shell 16 between impact events. Since theflexible fluid chambers are distributed around the circumference of head12, head 12 may be protected against the peak force of torsionalaccelerations as well as more complicated forms of impact. Thecompressible strengths of compressible material 24 may be from about 5 Gto 10 G in some embodiments.

Fluid passageways 20 may be sized based on fluid viscosity to establisha rate of fluid transfer during acceleration or deceleration to absorbimpact energy and to increase the time of the energy absorption processas mentioned above. In an embodiment, the fluid passageways may beflexible tubing. In another embodiment, the flexible fluid chambers andfluid interconnections may be formed from two or more sheets of aflexible polymeric material by welding patterns in the sheets definingthe chambers and associated fluid interconnections.

A side view of an embodiment of the invention is shown in FIG. 3. Outershell 16 of helmet 10 is shown attached to human head 12 by chinstrap 26and fastener 28. Releasing fastener 28 enables the wearer to removehelmet 10 from head 12. Other forms of securing helmet 10 to head 12 maybe used depending on the requirements of the application.

In another non-limiting embodiment, the fluid passageways may bearranged such that the damping is optimized for impact directions thatare not radial to the center of the head, but are instead torsionalaround the axis of the head. FIG. 4A shows a top view of helmet system130 on human head 112 inside helmet shell 116 with head 112 in a normalsymmetrical orientation with respect to helmet shell 116. Middle linerelements of helmet system 130 comprise flexible fluid chambers 118,interconnecting fluid passageways 120, and compressible material 124placed between the flexible fluid chambers 118 to center head 112 withinouter shell 116 (not shown) between impact events. Inner liner 122 formsthe inside layer of the helmet system 130. In contrast to the fluidpassageway layout of FIG. 2, fluid passageways 120 may be alignedparallel to and perpendicular to the major longitudinal axis of helmetshell 116.

FIG. 4B shows human head 112 rotated 25° counter-clockwise with respectto the normal orientation as a result of a torsional impact to helmetsystem 130. Flexible fluid chambers 118D and 118H have been compressedforcing fluid through passageways 120 to inflate chambers 118F and 118B,thereby cushioning head 112 when it rebounds after impact. A similarresult occurs when head 112 is rotated in a clockwise fashion after anappropriate torsional impact in an opposite direction. Such anarrangement is beneficial in certain sports and activities where thewearer is likely to experience off-angle impacts such as often seen inAmerican football. These impacts generate rapid rotations of the headcausing torsional distortion of the brain and resulting in MTBI evenwith lower levels of acceleration in the x, y, z direction. When thehelmet is exposed to rotational forces, the hydraulic damping systemdescribed herein may reduce the instantaneous force experienced by thewearer to a controlled level and increase the time over which theacceleration is experienced. This reduces the torsional forces coupledto the brain and may reduce the chance of MTBI caused by these forces.

In another embodiment, the fluid filled damping elements of theinvention may be made from at least three interconnected fluid chambers.An example is shown in FIGS. 5A and 5B. In helmet system 230, thedamping system is optimized for forces applied to the top of the head asindicated by arrow A and interacts with the spine as a downwardcompression along the Z-axis of the head. In this example, top chamber218A communicates with two other chambers, 218B and 218C, arrangedaround the bottom perimeter of helmet shell 216. An inner liner is notshown in FIGS. 5A and 5B. Such an arrangement may be beneficial incertain sports activities where the wearer is likely to experienceimpacts to the top of the head such as American football, bicycling,snow skiing and others. In American football, for example, two playersrunning toward each other with their heads lowered may experience headto head impact. Fluid forced from top chamber 218A to lower chambers218B and 218C over a time interval dependent on fluid flow rates andfluid interconnections 220 may positively impact the impact dynamicsexperienced by brain 214. As mentioned earlier, fluid interconnectionsbetween other fluid chambers in the helmet may also effect damping ofradial and rotational accelerations induced by off-center impact events.

In another embodiment, the fluid chambers may have more than a singlesize of fluid communication connections. Such secondary communicationpaths may allow different levels of restriction to motion in differentdirections. This may enable a designer to tailor the directional dampingresponse to anticipated forces experienced by the wearer. An example ofthis is shown in FIG. 6A and 6B which are a side view and a rear view ofthe embodiment of helmet system 330 positioned on human head 312respectively. Top fluid chamber 318A is connected to right and leftbottom fluid chambers 318B and 318C respectively by fluidinterconnections 320 and to rear fluid chamber 318D by fluidinterconnection 321. In the particular case of helmet system 330, rearfluid interconnection 321 has a smaller diameter than fluidinterconnection 320 which will provide a different dynamic response ofchamber 318D to the other two chambers thereby offering tunable responseof the fluid chamber system to an impact. An inner liner is not shown inFIGS. 6A and 6B.

In an embodiment, the fluids in some or all of the fluid chambers may bedilatant fluids. Dilatant fluids are non-newtonian in which theviscosity increases with the rate of shear strain. In the helmets of theinvention, these fluids provide greater damping when the appliedacceleration forces are greater. This enables the helmet to be usefulover a greater range of anticipated accelerations. The remaining designelements of other embodiments may remain unchanged when this variableviscosity fluid embodiment is incorporated.

In other embodiments, some or all of the fluid chamber sets may have ahigher or lower viscosity than other sets within the helmet. This mayprovide the ability to have different damping rates and differentacceleration directions while maintaining more constant fluid chamberthicknesses.

In another embodiment, the helmet may not incorporate a hard shell 16.Hard shell 16 may be necessary when likely objects of impact necessitatea hard shell to resist transference of energy from a rigid shape withreduced surface contact area. Other uses may not anticipate this type ofimpact event and therefore may not require a hard shell. A hard shellmay reduce protection in certain situations. For example, inwakeboarding and waterskiing a likely collision with water will occur atspeeds in excess of 20 mph. At these speeds there is a risk that thehard shell of a helmet may catch its edge on the water surfacetransferring breaking forces to the head and neck. In this case a riskof whiplash injuries may outweigh the risk of impacts with sharpsurfaces that would have required the use of hard shell protection. Asimpact velocity increases, a requirement for protection from impact withthe surface of the water may become important and the hard shellembodiment may be preferred.

In a soft shell embodiment, the use of interconnected fluid filledchambers, remains the same, but the shell may be a form-fittingcompliant cover. This cover may not allow the development of significanthydrodynamic forces at the interface of a helmet and water surface. Thismay be the preferred embodiment for use in sports including surfing,wakeboarding, wakesurfing, waterskiing and other compliant shell helmetexamples.

Hybrid embodiments combining portions of hard and soft shell embodimentsmay also be useful for watersports based on anticipated velocities andlikely impact surfaces. A typical example of an activity where themerits of soft shell and hard shell designs may be considered is cabletowed wakeboarding where there are solid objects such as metal rails into which the rider may collide. Based on likely impact velocities andimpact surfaces the selection of a hard shell or a hybrid embodiment maybe preferred.

An example of a hybrid embodiment is a helmet that contains both thehydraulic system described herein combined with a helmet liner made fromnon-resilient compressible materials that permanently deforms at forcelevels from about 60 G to about 150 G. In this embodiment, the hydraulicsystem may protect the head in lower speed impacts while thenon-resilient system may provide additional protection in higher speedimpacts by setting a maximum acceleration level for the protecting shellto deform and absorb impact forces. An example of this embodiment isshown in FIG. 7. Hybrid helmet system 430 comprises non-resilientcrushable inner liner 423 supporting fluid filled flexible fluidchambers 418A and 418E connected by fluid passageway 420. Flexible outerliner 422 closely covers the hydraulic impact resistance system and the_G resistant crushable inner liner 423 providing impact absorbingprotection to impacts exceeding _G. In all cases overall helmetperformance may be improved because of the reduced initial accelerationand impulse lengthening time associated with the hydraulic helmet linersystem.

Candidate materials for outer shell 16 of the various embodimentsdescribed herein may include impact resistant materials such aspolycarbonate, fiberglass, or Kevlar. An acceptable hardness for animpact resistant outer shell may be greater than Rockwell N62. Candidatematerials for flexible inner or outer shells may be elastomer,elastomeric polymer, polymer impregnated fabric, elastomer impregnatedfabric, laminated fabric, polymer fiber composite, leather, syntheticleather or others known in the art. Candidate materials for flexiblepads 24 between flexible fluid chambers 18 may include open cell andclosed cell foam made from synthetic materials including silicone andpolyurethane. Candidate materials for non-resilient crushable innerliner 423 may include expanded polystyrene, expanded polypropylene, orexpanded polyurethane.

In all embodiments described herein, the damping forces may be adjustedby means of fluid flow control. The dynamic interactions of hydraulicsystems are well established and understood, therefore only a briefdescription of how this invention uses hydraulic means to reduceinjurious forces is provided herein.

There is a relationship between applied force and hydraulic pressurethat is based on the surface area of the fluid chamber. Simply put, ifthe chamber has 2 in.² of surface and a force of 10 lbs. is applied, ahydraulic pressure of 5 psi. is generated. Increasing the chambersurface area reduces the hydraulic pressure while increasing the volumeof fluid being displaced. Reducing the surface area likewise increasesthe resultant pressure while reducing the volume of fluid beingdisplaced. Using this relationship, a designer can select the qualityand sizes of the chambers to control the hydraulic pressure during aprotective event.

There is a relationship between the size of the communication channel(tube) and the flow at any given pressure. Simply put, for any givenpressure a larger tube will allow more fluid and a smaller tube willallow less fluid to flow.

Finally there is a relationship between fluid viscosity and flow. Thethicker the fluid the slower the fluid will flow through a given size oftube at a given pressure.

In practice, the size of individual fluid chambers is based on thestrength of the chamber materials to ensure that the parts do not fail.The fluid is selected based on safety, cost and availability, viscosity,as well as compatibility with the materials used and the operatingenvironment of the helmets. The communication tubes are sized based onthe desired flow rate. The hydraulic helmet system described herein isdesigned to reduce the peak force levels and lengthen the period overwhich the forces are experienced such that stimulation of naturalresonant frequency of the brain is reduced. Since there are multipleenergy dissipation pathways, the protection can be adjusted to anynumber of requirements based on the particular impact characteristicsexpected, which will differ in different sports and applications. Thespecific arrangement of fluid chambers, communication channels, andfluid composition will be different in helmets optimized for differentsports. A helmet designed for use in bicycling may not be suitable foruse in American football and vice versa.

A method of forming helmet 10 according to an embodiment of theinvention is shown in FIG. 8. Method 530 comprises forming outer shell16 (step 531). Outer shell 16 may be a hard impact resistant shell thatis larger than head 12, or may be a flexible shell that is larger thanhead 12. In an embodiment, a preferred hard impact resistant shellmaterial may be a polycarbonate polymer with a Rockwell M hardnessgreater than 62. In another embodiment, a preferred flexible shellmaterial may be a synthetic leather. The method may also include formingfluidly connected flexible fluid chambers for installation in the spacebetween the outer and inner shells of the helmet (step 532). Theflexible fluid chambers are designed to contain liquids of differentviscosities depending on the application. Each fluidly connectedflexible fluid chamber group is connected by tubing of various diametersdepending on the anticipated functions of the helmet (step 533).Examples of suitable flexible tubing include vinyl, PVC, silicone, andothers. In an embodiment, the chambers and interconnected tubes may bemade from the same sheets of material with the size and shape of thechambers and fluid passageways established by pattern welding sheets ofthe material together. The interconnected bladders may then be filledwith fluid (step 534). Suitable fluids for the invention include water,glycerin, mineral oils, ethylene glycol and others known and not knownin the art. Flexible pads may then be formed for installation next tothe flexible fluid chambers to fix the location of the flexible fluidchambers in the space between the outer and inner shells of the helmet(step 535). In an embodiment, the pads may be designed to deform underimpacts exceeding about 5 G to 10 G. Candidate materials include opencell and closed cell foam made from synthetic materials includingsilicone and polyurethane. In the next step an inner shell may be formed(step 536). The inner shell may be a flexible material that conformsclosely to the head of the wearer. Materials suitable for an inner shellmay include the above materials noted for the flexible outer shell.

Assembling the helmet may include attaching interconnected flexiblefluid chambers and flexible pads to the outer and inner shells in thespace between the shells to form the helmet (step 537). In the finalstep, a chinstrap and connector may be attached to the outer and innershells to form the finished helmet (538).

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the invention without departing from the essentialscope thereof. Therefore, it is intended that the invention not belimited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A helmet configured to protect a human head against mild traumaticbrain injury upon impact comprising: an outer shell; a liner inside theouter shell, the liner comprising fluid fillable flexible fluid chambersfluidly connected to at least one other chamber by fluid connectionstherebetween, wherein the fluid fillable flexible fluid chambers arelocated around a circumference of the helmet and configured to fill aspace between the head and the outer shell when the helmet is positionedon the head; impact resistant flexible pads inside and spaced around aninner circumference of the outer shell adjacent to each of the fluidfillable flexible fluid chambers; and a flexible inner shell inside theliner, configured to fit on the head; the flexible fluid chambers beingconfigured to compress in response to impacting of the helmet on animpact side, and to force fluids through the fluid connections toinflate fluid chambers in other regions of the helmet, therebycushioning the head against a rebound from normal impacts, tangentialimpacts and mixtures thereof.
 2. The helmet of claim 1, wherein thefluid fillable flexible fluid chambers are fluidly connected to at leasttwo other fluid chambers by fluid connections therebetween.
 3. Thehelmet of claim 1, wherein the fluid connections are sized based onfluid viscosity to establish a rate of fluid transfer during impact toabsorb impact energy and lengthen a time of energy absorption to reducean effective frequency of energy transfer.
 4. The helmet of claim 3wherein the fluids comprise dilatant fluids.
 5. The helmet of claim 1,wherein the outer shell is a hard material with a hardness greater thanRockwell M
 62. 6. The helmet of claim 4, wherein the outer shell iscomposed of polycarbonate, fiberglass or Kevlar.
 7. The helmet of claim1, wherein the outer shell is a compliant material.
 8. The helmet ofclaim 1 wherein the inner shell is an impact resistant layer comprisinga non-resilient compressible material that permanently deforms at forcelevels from 60 G to 150 G.
 9. The helmet of claim 1, wherein the impactresistant pads are resistant to forces of 5 G to 10 G.
 10. The helmet ofclaim 1, wherein the inner shell is composed of elastomer, elastomericpolymer, polymer impregnated fabric, elastomer impregnated fabric,laminated fabric, polymer fiber composite, leather, synthetic leather ormixtures thereof.
 11. A method of forming a helmet to protect a humanhead against mild traumatic brain injury upon impact comprising: formingan outer shell larger than the head; forming a liner comprising fluidfillable flexible fluid chambers fluidly connected to at least one otherchamber that fit inside the outer shell around the circumference of thehelmet, the flexible fluid chambers being configured to fill a spacebetween the head and the outer shell when the helmet is positioned onthe head; connecting each group of flexible fluid chambers with a fluidconnection, so that each group of flexible fluid chambers isinterconnected; filling the groups of interconnected flexible fluidchambers with fluid; forming impact resistant flexible pads in the linerspaced around an inner circumference of the outer shell adjacent to eachof the flexible fluid chambers; forming a flexible inner shell insidethe liner, configured to fit closely on the head; attaching the flexiblefluid chambers and flexible pads to the inner and outer shells to formthe helmet such that the flexible fluid chambers are configured tocompress in response to impacting of the helmet on an impact side, andforce liquid through the fluid connections to inflate other fluidchambers in the helmet, thereby cushioning the head against a reboundimpact on helmet; and attaching a chin strap and fastener to the helmet.12. The helmet of claim 11 wherein the fluid fillable flexible fluidchambers are fluidly connected to at least two other fluid chambers byfluid connections there between.
 13. The method of claim 11 wherein thefluid connections are sized based on fluid viscosity to establish a rateof fluid transfer during impact to absorb impact energy and lengthen atime of energy absorption to reduce an effective frequency of energytransfer.
 14. The method of claim 11 wherein the fluids comprisedilatant fluids.
 15. The method of claim 11, wherein the outer shellmaterial is a hard material with a hardness greater than Rockwell M 62.16. The method of claim 15, wherein the outer shell is composed ofpolycarbonate, fiberglass or Kevlar.
 17. The method of claim 11, whereinthe outer shell is a compliant material.
 18. The method of claim 11wherein the inner shell is an impact resistant layer comprising anon-resilient compressible material that permanently deforms at forcelevels from 60 G to 150 G.
 19. The method of claim 16, wherein the outershell is composed of elastomer, elastomeric polymer, polymer impregnatedfabric, elastomer impregnated fabric, laminated fabric, polymer fibercomposite, leather, synthetic leather or mixtures thereof.
 20. Thehelmet of claim 11, wherein the impact resistant pads are resistant toforces of 5 G to 10 G.
 21. The helmet of claim 11, wherein the flexiblefluid chambers are filled with water, mineral oil, or mixtures of waterand non-toxic antifreeze liquids.
 22. The method of claim 11, whereinthe flexible fluid chambers and fluid connections are each produced fromtwo or more sheets of polymeric material by welding the sheets along apattern defining the flexible fluid chamber and fluid connection.